Optical and Photoelectrical Properties of β‐Rhombohedral Boron II. Photoeffects

Lü

Applied Physics Letters

et al. 2012

Magnesium-doped boron nanoswords were synthesized via a thermoreduction method. The as-prepared nanoswords are single crystalline and β-rhombohedral (β-rh) phase. Electrical transport measurements show that variable range hopping conductivity increases with temperature, and carrier mobility has a greater influence than carrier concentration. These results are consistent with the three dimensional Mott’s model (M. Cutler and N. F. Mott, Phys. Rev. 181, 1336 (1969)) besides a high density of localized states at the Fermi level compared with bulk β-rh boron. Conductivity of Mg-doped boron nanoswords is significantly lower than that of “pure” (free of magnesium) boron nanoswords. Electron energy loss spectroscopy studies confirm that the poorer conductivity arises from silicon against magnesium doping.

supporting

confidence: 81%

Influence of Si Co-doping on electrical transport properties of magnesium-doped boron nanoswords

Lü

Applied Physics Letters

et al. 2012

“…These are summarized in Ref. [13,14] and include changes in photoabsorption spectra [15], internal friction [16] and dielectric properties [17,18].…”

Section: Discussionmentioning

confidence: 99%

Relative stability of α and β boron

Widom

Mihalkovič

2009

J. Phys.: Conf. Ser.

α and β rhombohedral boron are closely related structures with nearly identical stability. Unlike α, in which every site is fully occupied, β is characterized by partial occupancy and intrinsic disorder. Optimizing the site occupation yields a superstructure of β that we call β . Its energy is lower than α but its symmetry lower than β. The configurational entropy of partial occupation drives a β → β transition around room temperature. Comparing the vibrational density of states, we find that β has an excess of low frequency modes that are strongly localized around the partially occupied sites. The vibrational entropy of these low frequency modes adds to the configurational entropy of partial occupation to further stabilize the β structure compared to α.

Physica Status Solidi (b)

“…E l c because of the small anisotropy and the very good agreement with the edge absorption of polycrystalline boron [6], i t seems to be possible to take those results into consideration, This leads to the assumption of indirect transitions connected with phonon emission (Debye temperatures of the concerned phonons: Oul = = (860 10) K, OD2 = (374 20) K [el) and to the indirect band gaps: 0.05 f 0.02 1 : AE, AE, (eV) I 1.39 & 0.03 I 134 & 0.03The difference of the absorption spectra of both crystals in the range of the edge tails(Fig. 8)gives the energy dependence of the additional absorption process, which shows a preferred efficiency with the orientation E I I c. A satisfactory adaption to the theory of Eagles El81 on the direct excitation of deeplying donor levels into the conduction band, as has been made in the case of trapping levels in boron[19], is not possible. But it is remarkable that in a fairly large range (0.5 to 0.95 eV) the absorption can be fitted to the t,heoretically expected variation of indirect interband transitions.…”

mentioning

confidence: 81%

Optical Anisotropy of β‐Rhombohedral Boron from 0.4 to 16 μm

Werheit

Hausen

Binnenbruck

1972

Self Cite

I n the intrinsic range the anisotropy of the reflectivity amounts to about 2% while the dichroism is very small at high photon energies and can only be measured when a & 2 x X lo3 cm-l. Especially distinct is the anisotropy of the lattice vibrations. Similar to polycrystalline boron two indirect interband transitions occur; the energy gaps are 1.561 and 1.39 eV with E 11 c and 1.541 and 1.34 eV with E 1 c. The edge tail is dominated by an absorption band, which is possibly caused by C or Si impurities.Im Bereich der Eigenabsorption betragt die Anisotropie des Reflexionsvermogens etwa 2%, wahrend der Dichroismus im Bereich hoherer Photonenenergien sehr klein ist und erst bei Absorptionswerten a 2 x lo3 cm-l meBbar wird. Die Anisotropie der Gitterschwingungen ist jedoch sehr ausgepragt. Wie in polykristallinem Bor treten zwei indirekte Interbandiibergange auf; die Bandabsttnde betragen fur E 11 c 1,561 und 1,39 eV, fur E 1 c 1,541 und 1,34 eV. Der Kantenauslaufer wird von einer Absorptionsbande beherrscht, die wahrscheinlich auf Coder Si-Verunreinigungen zuruckzufuhren ist.